This invention relates to a contact screen for making color separation halftone blocks, for use in a picture reproducing machine such as a color scanner.
In a color scanner, as is well-known, an original picture mounted to a picture cylinder is scanned photoelectrically by a picture scanning head to obtain color separation picture signals which are to be stored in parallel in a memory, and then by using the color separation picture signals read out of the memory in series, color separation reproduction pictures are recorded by a recording head on a photosensitive material mounted to a recording cylinder. For example, Japanese Patent Publication No. 52-18601, titled "A color separation reproduction picture recording method", has been filed by the same applicant and assignee as the present invention.
In FIG. 1 there is shown a color scanner including picture cylinder 1 on which an original picture 2 is mounted, and a recording cylinder 3 on which a photosensitive material 4 is mounted. Color separation reproduction pictures 5K, 5M, 5C and 5Y for black, magenta, cyan and yellow colors are recorded on the photosensitive material 4, as described above.
A contact screen comprising four halftone screens, each having a different screen angle, which are coupled to one another in series, to reproduce the color separation reproduction pictures in the color scanner, has been disclosed and claimed in a filed Japanese Utility Model Laying-Open Specification No. 49-128114 (Japanese Utility Model Application No. 48-25774) by the same applicant and assignee as the present invention.
In FIG. 2 is shown such a contact screen 6 which is rolled onto the photosensitive material 4 which is mounted to the recording cylinder 3 of FIG. 1, and comprises four halftone screens 7K, 7M, 7C and 7Y having screen angles of 45.degree., 15.degree., 75.degree. and 0.degree., respectively, for black, magenta, cyan and yellow colors, which are connected in a row.
This contact screen 6 is conveniently used in a color scanner having a similar construction to the one shown in FIG. 1. However, in order to improve the operational functions, a conventional color scanner is provided with a function which is capable of projecting register marks, together with the color separation reproduction pictures. The register marks are used for positioning the color separation films or blocks when a color reproduction picture is reproduced.
For example, in FIG. 3 there is shown a recording photosensitive material 8 on which the color separation reproduction pictures 9 are to be recorded. Lattice-shape images 10 are recorded on the photosensitive material 8 in its blank spaces above, below and between the color separation reproduction pictures 9. The lattice-shape images 10 comprise transverse and longitudinal register lines crossing one another, and are used as register marks. This is disclosed in Japanese Patent Laying-Open Specification No. 54-46602, or Japanese Patent Application No. 52-113046, which has been filed by the same applicant and assignee as the present invention.
If the color separation reproduction pictures and the lattice-shape register lines shown in FIG. 3 are recorded simultaneously on the photosensitive material by projection through the contact screen shown in FIG. 2, the register lines thus recorded will be in the form of the halftone "dots". Since the images are broken up through the contact screen, the recorded images will involve jagged or rugged edges in their outlines. What is worse, since the screen angle of each reproduction picture is different, the jagged or rugged edges of the register lines are in disorder.
Register lines should be recorded in straight, solid lines. When register lines having the jagged or rugged edges are used, the accuracy of the positioning of the picture films is deteriorated. In particular, in an automatic positioning machine for picture films which operates by detecting photoelectrically register marks formed thereon, the register marks should be straight solid lines. If the optical resolution is high, it becomes extremely difficult to register lines which are comprised of halftone dots.